Plasma deposited selective wetting material

ABSTRACT

A selective wetting material is formed by plasma depositing a film on a substrate from a two-component reaction of a silicon donor and organic precursor, and photo-oxidizing selected regions of the deposited film to form wetting regions to which a liquid will selectively adhere. When the liquid is an electrically conductive material, the process may be used to form printed circuits on a circuit board. When the substrate is optically transparent and the non-photo-oxidized regions of the film are removed, the process may be used to form a photomask.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/045,314,filed Jan. 14, 2002 now U.S. Pat. No. 6,764,812, which is acontinuation-in-part of U.S. application Ser. No. 09/435,396, filed Nov.6, 1999, now U.S. Pat. No. 6,416,938, which is a continuation-in-part ofU.S. application Ser. No. 08/873,513, filed Jun. 12, 1997, nowabandoned, which claims the benefit of U.S. Provisional Application No.60/020,392, filed Jun. 25, 1996, each of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The invention relates generally to the formation of photosensitiveorganosilicon films by plasma-initiated polymerization utilizing directapplication of electrical energy, and more particularly, to theformation of photosensitive films from a silicon donor and an organicprecursor for use as a selective wetting material.

BACKGROUND OF THE INVENTION

Selective wetting materials can be used in applications associated withthe fabrication of electrical circuits.

An integrated circuit is a three-dimensional structure of alternatingpatterned layers of conductors, dielectrics and semiconductor films. Thepatterned layers are formed by lithographic processes that consist oftwo steps: delineation of the patterns in a radiation sensitivematerial, usually a polymer; and transfer of the patterns intounderlying, previously deposited thin films, using an appropriateetching technique.

Conventional photolithography (that is, photolithography employing lightat 350 to 450 nm wavelength) is used to fabricate solid-state deviceswith features of 6 μm or smaller. Incremental improvements have allowedthe use of light in the range of 350 to 450 nm wavelength to produceever smaller features. However, the ultimate resolution of a printingtechnique is governed, at the extreme, by the wavelength of the light,or radiation, used to form the image, with shorter wavelengths yieldinghigher resolution. The same physical principles also govern theresolution limits in microscopy. Additionally, the same basic positivephotoresist, consisting of a photoactive compound that belongs to thediazonaphthoquinone chemical family and a novolac resin, has been inpervasive use since the mid-nineteen seventies, and will likely be theresist of choice for several more years. The manufacturing facility hasalso been driven to cleaner specifications due to the smaller geometriesof the parts being produced. The cost of introducing a newphotolithographic technology, which includes the cost associated withthe development and implementation of new hardware and resist materials,is a strong force pushing refinement of current photolithographicprocesses and conventional clean room design instead of pursuingrevolutionary techniques. The technological alternatives to conventionalphotolithography are largely the same as they were a decade ago: shortwavelengths of light (220 to 280 nm), the so-called deep ultravioletrange photolithography; scanning or projection electron beam; and x-rayor scanning ion beam lithography.

Unfortunately, conventional resists are not appropriate for use with thenew lithographic technologies that are necessary for producing linewidths under 0.5 μm. The most notable deficiencies of the conventionalnovolac-quinonediazide resists are their sensitivity and absorptioncharacteristics. Additionally, the absorption of conventionalphotoresists is too high to allow uniform imaging through practicalresist film thicknesses (approximately equal to 1 μm). Thus, no matterwhich technology becomes dominant after photolithography has reached itsresolution limit (that is, 0.3 to 0.5 μm), new resists and processeswill be required, necessitating enormous investments in research andprocess development. The introduction of new resist materials andprocesses will also require a considerable lead time to bring them tothe performance level currently realized by conventional positivephotoresists. Clearly, conventional wet chemistry photoresists havelimited applicability for the future of solid-state device fabrication.Liquid resist chemicals are very difficult to obtain in a pure state andare expensive. The process of applying a wet resist does not lend itselfto large or odd shaped substrates, and the required baking step makesthis process unsuitable for temperature sensitive substrates.

Consequently, there are advantages to a photoresist which is easilyapplied and processed in a vacuum chamber or series of enclosed chamberswith no requirement for being brought to atmosphere. Such a photoresistpermits the elimination of wet chemistry processes, and consequently,provides substantial benefits in the reduction of costs and generationof hazardous wastes. Furthermore, it eliminates the exposure ofoperators to the hazardous liquids and vapors generated by theconventional resist process. Finally, the dry plasma depositedphotoresist allows the further development of integrated manufacturingmodules without the necessity of clean rooms.

Despite intensive research on the plasma deposition of amorphous siliconfrom monosilane (SiH₄), there have been only a few reports exploring theformation of Si—Si bonded polymers from monosubstituted organosilanes.Haller reported an example of selective dehydrogenative polymerization,but no photochemical studies were described. See Haller, Journal of theElectrochemical Society A, Vol. 129, 1987, p.180, and Inagaki and Hirao,Journal of Polymer Science A, Vol. 24, 1986, p. 595. Studies on theplasma chemistry of methylsilane (MeSiH₃) have involved higherradio-frequency powers and temperatures which promote formation ofamorphous silicon carbide (SiC) rather than reactive polymeric product.See Delpancke, Powers, Vandertop and Somorjai, Thin Solid Films, Vol.202, 1991, p. 289. Low power plasma polymerization of tetramethylsilaneand related precursors has been proposed to result in the formation ofSi—C—Si linkages. See Wrobei and Wertneimer, Plasma Deposition,Treatment and Etching of Polymers, Academic Press, New York, Chapter 3.Such materials lack sufficient absorption in light above approximately225 nm wavelength, but have been studied as far ultraviolet (193 nmwavelength) resists by Horn and associates. See Hom, Pang andRothschild, Journal of Vacuum Science Technology B, Vol. 8, 1991, p.1493. Polymer chemistry teaches the use of the basic silanes areinsignificant as a monomer for polymerization type of polymer.Furthermore, polysiloxanes are differentiated from the basic silanes,and contrasted as being very important in terms of monomers forpolymerization. See Stevens, Malcom P., Polymer Chemistry, AnIntroduction, Addison-Wesley Publishing Co., 1975: p. 334. As usedherein, polymerization is the process whereby monomers are boundtogether forming various length chains but essentially repeating thebasic building block of the monomer without significant chemical orphysical alteration of the beginning monomer.

Work has been reported on the synthesis of soluble poly-alkylsilynenetwork polymers ([SiR]_(n)) which exhibit intense ultravioletabsorption (associated with extended Si—Si bonding) and may bephoto-oxidatively patterned to give stable siloxane networks. SeeBianconi and Weidman, Journal of the American Chemical Society, Vol.110, 1988, p. 2341. Dry development is accomplished by selectiveanisotropic removal of unexposed material by chlorine or hydrobromicacid reactive ion etching. See Hornak, Weidman and Kwock, Journal ofApplied Physics, Vol. 67,1990, p. 2235, and Horn, Pang and Rothschild,Journal of Vacuum Science Technology B, Vol. 8, 1991, p. 1493. Theexposed, oxidized material may be removed by either wet or dry fluorinebased chemistry. Kunz and associates have shown that this makespolysilynes particularly effective as 193 nm wavelength photoresists.See Kunz, Bianconi, Horn, Paladugu, Shaver, Smith, and Freed,Proceedings of the Society of Photo-optical and InstrumentationEngineers, Vol.218, 1991, p. 1466. The high absorbability and thewavelength limits photo-oxidation to the surface, eliminatingreflection, and the pattern is transferred through the remainder of thefilm during the reactive ion etch (RIE) development. Studies oforganosilicon hydride network materials containing reactive R—Si—Hmoieties have found that such high silicon compositions as[MeSiH_(0.5)]_(n) exhibit superior photosensitivity and function assingle layer photodefinable glass etch masks. See Weidman and Joshi, NewPhotodefinable Glass Etch Masks for Entirely Dry Photolithography:Plasma Deposited Organosilicon Hydride Polymers, Applied PhysicsLetters, Vol. 62, No. 4, 1993, p. 372. However, cost and availability ofthe exotic organosilicon feedstocks have significantly inhibited thetransfer of such photosensitive organosilicon hydride network materialsinto microcircuit fabrication. Further, films deposited from singlecomponent organosilicon feedstocks possess limited latitude inalteration of deposited film characteristics, such as the radiationfrequency of photosensitivity and selectivity during etch processes.

Organosilicons have been used to produce various types of films, asdisclosed by the following references.

U.S. Pat. No. Name Date 4,493,855 Sachdev et al. January 1985 4,532,150Endo, et al. July 1985 4,868,096 Nakayama et al. September 19895,294,464 Geisler et al. March 1994Sachdev et al. teaches the deposition of an organosilicon film by plasmapolymerizations. However, the deposited film is not itselfphotosensitive. Sachdev et al. uses the film as a barrier and uses aconventional spun-on resist to pattern it. Sachdev et al. does not teachthe use of a plasma-deposited film as a photoresist; a conventionalphotoresist is used to pattern the plasma-deposited film, which is thenused as an etch mask. Endo et al. describes the plasma deposition of asilicon carbide layer. A single organosilicon gas that may react withother materials is used to deposit a durable silicon carbide type offilm. Furthermore, Endo et al. does not teach film photosensitivity.Nakayama et al. discloses the use of an oxygen plasma to modify asilicon surface to allow a conventional photoresist to adhere to thematerial. The conventional photoresist is then used to pattern thesilicon layer. A photosensitive organosilicon film is not deposited.There is no plasma depositing of a film; the oxygen plasma is used tomodify the surface structure which is followed with conventionaltechniques for patterning the silicon film. Geisler et al. describes amethod of plasma-coating a plastic substrate using organosiloxanes andan inert gas to facilitate adhesion of a reflective layer of a metalwith minimal surface damage to the substrate. None of these referencesteach a selective wetting material formed from a photosensitive plasmapolymerized organosilicon film produced from a two-component plasmareaction wherein the first component comprises a silicon donor that isnon-carbon containing and non-oxygenated and the second componentcomprises an organic precursor that is non-silicon containing andnon-oxygenated, with selective regions of the film being photo-oxidizedto produce a selective wetting material that when brought in contactwith a liquid, the liquid will selectively wet and adhere to thephoto-oxidized regions of the film, and will not adhere to thenon-photo-oxidized regions of the film.

A conventional circuit board is produced by depositing an electricallyconductive material, such as silver, on the surface of a substrate (orcircuit board) formed from an electrically insulated material, such as aglass epoxy laminate. Selected regions of the deposited electricallyconductive material are removed by etching in a patterning process thatcan be accomplished by photolithography. The remaining regions ofelectrically conductive material form the printed conductors on thecircuit board. The process is inefficient in that the entire surface ofthe board is first coated with the electrically conductive material, andthen some of the deposited material must be removed to define theprinted circuit paths or conductors on the board. Therefore there is theneed for a process that can form printed circuits on the board withoutfirst blanket coating of the board with the electrically conductivematerial and then selectively removing regions of the electricallyconductive material.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a process for forming aplasma-deposited selective wetting material on a substrate by forming aphotosensitive film on a substrate from a two-component plasma reaction.The first component comprises a non-carbon containing and non-oxygenatedsilicon donor and the second component comprises a non-siliconcontaining and non-oxygenated organic precursor. The film is patternedwith radiated electromagnetic energy through a mask in the presence ofoxygen to produce a selective wetting material that has one or morephoto-oxidized regions. When the selective wetting material is placed incontact with a liquid, the liquid selectively wets and adheres to thephoto-oxidized regions and does not adhere to the non-photo-oxidizedregions.

When the liquid is an electrically conductive material, the depositionand drying of the liquid adhering to the photo-oxidized regions can formprinted circuits on a circuit board.

When the non-photo-oxidized regions of the selective wetting materialare removed and the substrate is an optically transparent material, thesubstrate with the remaining photo-oxidized regions covered by thedeposited and dried liquid can form a photomask.

Additional objects, advantages and other useful features of theinvention will become apparent to those skilled in this art from thefollowing description, wherein a preferred embodiment of this inventionis shown and described, simply by way of illustration of one of themodes best suited to carrying out the invention. As will be realized,the invention is capable of other and different embodiments, and itsseveral details are capable of modifications in various, obviousaspects, all without departing from the invention. Accordingly, thedescription is to be regarded as illustrative in nature, and notrestrictive. The objects and advantages of the invention may be realizedand attained by means of the processes particularly pointed out andclaimed in the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Plasma-deposited photosensitive polymer (PDPP) films used to produceselective wetting materials of the present invention are produced byflowing a silicon donor and an organic precursor into an evacuatedplasma chamber, wherein the donor and precursor react and deposit a PDPPfilm on a substrate in the chamber. Any plasma chamber with thefollowing characteristics would be suitable for the development of thesefilms:

(1) hardware for evacuating the chamber to eliminate the presence ofoxygen;

(2) electrodes supplied with electrical energy to sustain the plasma;

(3) hardware for flowing the silicon donor and organic precursor throughthe plasma chamber at controlled flow pressures; and

(4) hardware for holding the substrate on which the film is to bedeposited in position in the plasma chamber.

For the deposition of these particular films, a Model DSN RoomTemperature Plasma Deposition System, which is available from IonicSystems (San Jose, Calif.), was used. This plasma chamber issubstantially as disclosed in U.S. Pat. No. 4,262,631, withmodifications noted herein. The plasma chamber was equipped with dualpower supplies of 2,500 W and 1,000 W that operated at 13.56 MHz. Theplasma chamber was vacuum pumped with an Edwards High VacuumInternational (Wilmington, Mass.) Model E2M-80 direct drive rotary vanepump. Flow pressures were monitored with an M K S Instruments, Inc.(Andover, Mass.) Series 220 BARATRON.

The materials used as silicon donor and organic precursor must be in agaseous or vapor state to achieve flow through the plasma chamber.Selection of materials for the silicon donor and organic precursor willbe dependent upon the desired characteristics of the PDPP film, the costof the materials, and how well-behaved the materials are in theprocessing environment.

The material used as a silicon donor is a substantially non-carboncontaining and non-oxygenated silicon compound. Silicon hydrides arepreferred since they provide more silicon, which enhances the use of thePDPP film as a resist in the fabrication of solid-state devices andother film product applications, such as selective wetting materials. Inone preferred embodiment of the invention, monosilane (SiH₄) is used asthe silicon donor. Other suitable source materials for silicon donorsinclude disilane (Si₂H₆) and dichlorosilane (SiH₂Cl₂).

The material used as an organic precursor is a substantially non-siliconcontaining and non-oxygenated organic compound. In these preferredembodiments, ethylene (C₂H₄), methane (CH₄) and ethane (C₂H₆) are usedas gaseous organic precursors, and toluene (C₆H₅CH₃) is used as a liquidvapor donor. Other suitable sources for organic precursors broadlyinclude organic compounds such as alkanes, alkenes, alkynes, phenyls andaromatic hydrocarbons. Selective organic compounds may be blended toachieve an optimum organic precursor for a desired PDPP filming process.

A film formed from a separate silicon donor and organic precursor leadsto a film product that is more easily produced and controlled in itscontent than film product from a single organosilicon feedstock.

In one preferred embodiment, monosilane is used as the silicon donor,and ethylene gas or toluene vapor is used as an organic precursor todeposit the PDPP film. Flow rates of monosilane have been used in therange of 20 to 200 scc/min (preferably 25 to 35 scc/min), and organicprecursors flowed at 100 to 300 scc/min (preferably 140 to 180 scc/min).Pressure in the plasma chamber has been allowed to build to 150 to 500mtorr (preferably in the range of 180 to 300 mtorr). Power fordeposition of the film has been applied in densities from 0.8 to 15mW/cc, with the optimum range being 8 to 10 mW/cc at 13.56 MHz. Theseoperating parameters will be understood by those skilled in the art astypical operating conditions and not as limiting the scope of theinvention.

The monosilane used was Semiconductor Grade Silane (SiH₄), which isavailable from Liquid Carbonic Industries Corp. (Oak Brook, Ill.).Organic precursors were 99.9% pure ethylene, supplied by Liquid CarbonicIndustries Corp., or ACS Certified Class 1B toluene, supplied by FisherChemicals (Fair Lawn, N.J.).

Selected organic precursor materials must have sufficient vaporpressure, with or without heating, to allow their introduction into theplasma chamber. This includes a variety of materials that can be eithera gas or liquid at standard temperature and pressure (STP). In mostcases, the exposure of a liquid organic precursor in a containmentvessel to the vacuum system will generate sufficient vapor flow to allowmany liquids, as well as gases, to be used with no operator exposure. Ifsufficient vapor pressure is not attained, the liquid donor may beheated slightly to increase its vapor pressure. For the processing ofthe films in one preferred embodiment, one gas at STP, ethylene, or oneliquid at STP, toluene, is used as the organic precursor. Toluene wasselected due to its favorable vapor pressure, as well as its ultraviolettransmission characteristics. Neither the silicon donor nor the organicprecursor can contain an appreciable amount of oxygen, since oxygen withultraviolet exposure from the plasma during the deposition process wouldcause photo-oxidation of the silicon and degrade the photosensitivity ofthe deposited film.

A silicon donor that is substantially non-carbon and non-oxygencontaining inhibits the polymerization of the silicon donor with theorganic precursor during the plasma reaction. This promotes the encasingof plasma-generated modified forms of the silicon donor that include(Si—H) and (Si—Si) low molecular weight fragments within an organicpolymer matrix formed substantially from plasma-polymerization of theorganic precursor. Therefore, photo-oxidation is achieved primarily bythe oxidation of the silicon within the interstitially situated modifiedforms of the silicon donor when the film is subjected to radiatedelectromagnetic energy.

For the monosilane/ethylene film depositions, ethylene was supplied toan inlet port on the plasma chamber and controlled with a manual flowvalve. A vessel was used for the containment of liquid toluene for themonosilane/toluene film depositions. The liquid nature of toluene at STPrequired the development of a method for the introduction of toluenevapors to the plasma chamber. A sample cylinder was obtained andthoroughly cleaned for the toluene introduction. After cleaning anddrying, the cylinder was attached to the deposition system and evacuatedto less that 10 mtorr. At this point, the valve on the sample cylinderwas closed and the cylinder removed from the system. A clean stainlesssteel tube was attached to the sample cylinder. The tube was submergedin a vessel of reagent grade toluene and the shut-off valve was opened.The vacuum inside the sample cylinder was used to draw the toluene intothe sample cylinder while introducing as little trapped gas as possible.After installation on the vacuum system, the shut-off valve was openedand the toluene was allowed to degas for fifteen minutes before anyplasma processing was attempted. Seasoning runs were performed for onehour before actual depositions were performed for the photosensitivefilms.

A water bath was installed on the liquid toluene vapor source to assistin keeping a constant vapor pressure during the depositions. No heatingwas used in the bath, but the temperature held at 23° C.±1° C. duringdepositions. Pressure during depositions held constant within ±5 mtorr.The effect of the evaporative cooling was minimal on the vapor pressureand flow of the liquid toluene donor. Flow from the vessel wascontrolled with a manually adjusted valve on the top of the containmentvessel. Initially, no attempt was made to either heat or hold the liquidvessel isothermal to reduce evaporative cooling, which would have animpact on the ability to maintain constant flow. However, pressureduring deposition was constantly monitored to determine if the flow ofthe toluene was dropping.

Initial depositions of the PDPP films were performed with the plasmachamber's depositor under manual control to easily vary and controldeposition conditions. A monosilane flow rate of 50 scc/min was used toestablish a plasma chamber pressure with the monosilane, and thenvarying amounts of organic precursors were flowed to achieve the desiredpressure increases. The ratio of the pressure of the organic precursorto the pressure of the monosilane was used for monitoring during thescreening. Weight ratios of organic precursor to monosilane of less than1:4 and greater than 2.5:1 resulted in films of negligiblephotosensitivity. For useful depositions, weight ratios of organicprecursor to monosilane of 1:2 and 1:1 were chosen. In addition, fordeposition, input power to the plasma chamber was varied between 200 Wand 400 W. PDPP films were successfully deposited on a variety oforganic and inorganic substrates with the disclosed process. Magneticsubstrates, either as a top deposition layer or other layer in thecomposite substrate, are not a preferred application since the magneticfield produced by the material, even if it is not the contact layer forthe film, has the potential of interfering with the structure of thefilm during the plasma polymerization process and thereby can influencethe photosensitivity throughout the thickness of the film.

It is preferable to separately flow the silicon donor and organicprecursor into the plasma chamber to enhance substantial uniformity ofthe plasma-modified silicon donors within the resulting organic polymermatrix and prevent possible spontaneous pre-reactions. As understood bythose skilled in the art, silicon donors and organic precursors can bepremixed in a variety of ratios to ensure uniform componentdistribution, and reduce the cost and complexity of the piping andassociated hardware for gas introduction into the plasma chamber. Donorsand precursors can also be premixed or mixed in a manifold. Premixing ofthe silicon donor and organic precursor is acceptable but may requirestricter process control to achieve a substantially uniform distributionwithin the film. Hydrogen or an inert gas may be added to increaseuniformity due to its higher mobility.

As understood by those skilled in the art, a variety of depositionsystems may be used that operate at a wide variety of power levels andtypes, including radio frequency range (approximately 40 kHz) throughmicrowave, and electron cyclotron resonance systems operating in excessof 2 GHz. In the preferred embodiments, there is no substrate heatinginvolved, but the substrate can be heated or cooled during thedeposition process to enhance the properties of the deposited films. Awide variety of pressures, from ultrahigh vacuum (less than 10⁻⁷ torr)up to and exceeding atmospheric pressure can be used. In the preferredplasma chamber, the substrate floats electrically, but it can begrounded or powered.

Samples of the PDPP films that were prepared by the above processes wereexposed to ultraviolet radiation in the presence of oxygen from the air.Exposures were performed at low resolution using UVP, Inc. (Upland,Calif.) Model No. UVG-54 ultraviolet source for use at 254 nmwavelength. Exposures at 365 nm wavelength were made using the same lamphousing with a UVP, Inc. Model No. 34-0034-01 ultraviolet source for useat 365 nm wavelength. Various masks were used for contact type imaging.

Developing was performed in a 10:1 Buffered Oxide Etch (10:1 BOE)supplied by Ashland Chemical Company (Columbus, Ohio). A composition forthis 10:1 Buffered Oxide Etch can be found in Ashland Chemical Company'sMaterial Safety Data Sheet No. 308.0034306-005.004I, which defines theingredients of the 10:1 BOE in percent by weight as: water (57.0-61.0%); ammonium fluoride (34.0-38.0 %); and hydrofluoric acid (4.7%).Film thicknesses were determined profilometrically with a SloanTechnology Corp. (Santa Barbara, Calif.) Dektak 1 and Nanometrics Inc.(Kanata, ON, Canada) Model 216S.

Photosensitivities were first observed after exposure to 254 nmwavelength deep ultraviolet with a simple contact mask. Development tookplace in a 10:1 BOE to establish that there was conversion of theplasma-deposited photosensitive polymer (PDPP) to the exposed glass-likeplasma-deposited photosensitive polymer (GLPDPP), and to establish etchrates.

The films deposited by the above disclosed processes had thicknesses of0.08 to 0.15 μm of PDPP. These film thicknesses are representative ofachievable film thicknesses and are not limiting as to the scope of theinvention. Development was performed in a 10:1 BOE. Except as noted inTable 1, there was selectivity exhibited between PDPP and GLPDPP, andthe GLPDPP was entirely removed from the silicon substrate as indicatedby profilometry.

TABLE 1 Data for PDPP Deposition, Photo-oxidation and Etching PartialPressure of the Organic Resultant Precursor Depo- Compressive BOERelative sition Stress in Etch Selectivity Sample Organic to SilanePower Rate Film Rate (GLPDPP: Number Precursor (%) (W) (Å/sec)(Dynes/cm²) (Å/min) PDPP) 1 Ethylene 50 400 0.82 2.7 × 10⁸ 140 NotDetected 2 Ethylene 50 200 0.71 8.3 × 10⁷ 210 Not Detected 3 Ethylene100  400 0.91 4.7 × 10⁸ 185 Not Detected 4 Ethylene 100  200 0.72 0.8 ×10⁸ 320 >25:1 5 Toluene 50 400 0.85 3.3 × 10⁸ 300 >25:1 6 Toluene 50 2000.83 7.6 × 10⁷ 330 >25:1 7 Toluene 100 400 0.88 2.1 × 10⁸ 285 >25:1 8Toluene 100 200 0.88 9.8 × 10⁷ 270 >25:1

For the results in Table 1, the monosilane flow rate for all depositionswas 50.0 scc/min and the pressure from monosilane flow was 68 to 70mtorr. Stress measurements were made on bare 1,0,0 silicon wafers. Allexposures were made with light at 248 nm wavelength for exposure dosageof 600 mj/sq-cm. Deposited film thickness was 1500 Å. Etch rates are fora 10:1 buffered oxide etch and are for the exposed (GLPDPP) area.Samples were monitored visually every minute during etching to determineetch rate. Samples with greater than 25:1 selectivity (GLPDPP:PDPPetching selectivity) exhibited no PDPP etching from the 10:1 BOE, andactually increased slightly in thickness due to swelling.

For Sample Numbers 1, 2 and 3 in Table 1, the etch selectivity is poor.The etch would not fully clear oxidized areas, and unexposed areas wereetching away almost as quickly as the exposed areas. For these samples,a combination of the deposition conditions, exposure conditions, andetchant used resulted in generally unsuitable structures. For sampleswith good selectivity, film fully converted to GLPDPP.

The use of the 10:1 BOE provides a benchmark for the etchability of theexposed material and further demonstrates that the exposed GLPDPP actslike a silicon oxide type material, while the unexposed PDPP was notaffected by the 10:1 BOE, as is consistent with a silicon hydridenetwork.

For use of the film of the present invention as a selective wettingmaterial, selective etching of unexposed, non-photo-oxidized PDPP filmis desirable in some applications as further described below. A simplechlorine based dry etch was used to remove unexposed PDPP while leavingthe exposed GLPDPP material. Operating conditions for the Zylin etchingmachine are identified in Table 2. Etching was performed with chlorineplasma dry etching, available from Liquid Carbonic Industries Corp. (OakBrook, Ill.). Results of the tests are listed in Table 3. Filmthicknesses were obtained using a Nanometrics (Kanata, ON, Canada)NANOSTEP. The apparent slight increase in film thickness after etchingthe unexposed areas is due to normal instrumental error. As can be seenby the results in Table 3, the selectivity in chlorine etch forunexpossed PDPP to exposed GLPDPP is greater than 15 to 1.

TABLE 2 Operating Conditions for Chlorine Etching Parameter SettingChamber Pressure 100 mtorr RF Power 150 W DC Bias 150 V Chlorine FlowRate  50 scc/min Electrode Temperature  40° C.

TABLE 3 Results of Chlorine Etching for PDPP/GLPDPP Film ExposedUnexposed Photo- Photo- Film Film sensitive sensitive ThicknessThickness Etch Sample Polymer Polymer Before After Etch Rate Number(GLPDPP) (PDPP) Etch (Å) (Å) (Å/min) 1 GLPDPP — 1712 1361 351 1 — PDPP1825 1836  0 2 GLPDPP — 1724 1406 318 2 — PDPP 1865 1871  0 3 GLPDPP —1699 1327 372 3 — PDPP 1812 1819  0

The above photo-oxidation and selective etching processes show how thePDPP film depositions from separate silicon and organic precursors canbe used as a resist material in the fabrication process for solid-statedevices and as a selective wetting material in applications wherein thenon-photo-oxidized regions of the film are removed. Table 4 illustratesachieved etching selectivites between unexposed PDPP and exposed GLPDPPwith various etching processes.

TABLE 4 Selective Etching of PDPP and GLPDPP Material Etch SelectivityMaterial (Material Etched: Material Not Material Not Etched EtchedEtched) Etching Process GLPDPP PDPP >50:1 10:1 Buffered Oxide GLPDPPPDPP >15:1 Fluorine Reactive Ion PDPP GLPDPP >50:1 Chlorine Reactive Ion

Photo-oxidation as used in this specification is generally understood tobe accomplished by the exposure of a material to radiatedelectromagnetic energy in the presence of oxygen in air. Generally,light energy is used, and more specifically, light in the ultravioletend of the visible electromagnetic spectrum, typically recognized asfrom 200 nm to 400 nm, is used. It will be understood by those skilledin the art that other forms of radiant energy, above visible light inthe electromagnetic spectrum, such as x-rays, or gamma or alpharadiation, may be used. Furthermore, since oxygen in the air is theagent for oxidation, other concentrations of oxygen can be used.

In the fabrication of a solid-state device, whether it is amicroprocessor, memory chip, liquid crystal display, pressure sensor,transistor, capacitor, resistor, and so forth, the production sequencesinclude the patterning of numerous substrate materials. Patterning istypically done by masking a substrate covered by a film of resist andexposing the resist to radiated electromagnetic energy, typicallyultraviolet light, through the mask. As further described below, theselective wetting material of the present invention may be used tofabricate the photomask. The mask permits only selected areas of theresist to be exposed to the ultraviolet light. Then, either the exposedor unexposed resist is selectively etched away in a process knows asdeveloping. One or more production processes, known to those skilled inthe art (see, e.g., Semiconductor and Integrated Circuit FabricationTechniques, Gise, Peter, and Blanchard, Richard, Fairchild Corporation,Reston Publishing Company, Reston, Va., 1979), such as: etching of thesubstrate; pattern or image transfer from the mask to the resist, andthen to the substrate; diffusion of a material into a substrate layer;ion implanting in a substrate layer; pigment injection or dyeing of asubstrate layer, is then performed. Subsequently, the remaining resistis removed, and the process is repeated as required to fabricate thedevice. The art of microlithography with conventional chemistries iswell known in the art. For a typical silicon based integrated circuit, asilicon dioxide film, or substrate, is grown on a silicon wafer to actas an insulator. Using the disclosed filming process, a PDPP film isdeposited on the silicon dioxide. Areas of the silicon dioxide that areto be removed for implant of material into the silicon are patterned.The PDPP is exposed to ultraviolet light through a mask which delineatesthe required patterning. Using a fluorine reactive ion etch, the GLPDPPproduced by exposing the PDPP to ultraviolet light through the mask inthe presence of oxygen is etched away, and the production process ofetching away the silicon dioxide is also performed. As indicated inTable 5, the fluorine reactive ion etch will etch silicon dioxide at arate 30 times as great as it will etch PDPP. The PDPP is removed andselected material is implanted into the silicon wafer through thepatterned silicon dioxide substrate. This process of substrate layering,patterning, and performing production processes is repeated as requiredto fabricate each circuit device, as well known in the art withconventional chemistries. Both silicon and silicon oxide can beselectively patterned with the PDPP and GLPDPP as shown in Table 5.Finally, interconnection of the individual circuit devices can be donewith a metal, usually aluminum. Patterning of the aluminum can also bedone with the PDPP/GLPDPP process. A layer of silicon nitride is placedover the top of the fabricated device for protection. The PDPP/GLPDPPprocess is also used to pattern the silicon nitride to expose thealuminum pads for external circuit connections. The describedfabrication process is typical whether the device is a simple discretetransistor, a microprocessor, dynamic random access memory device, orthe driver transistors for a liquid crystal display. In generalalternating layers, or substrates, of semiconductors, insulators andconductors are deposited and patterned to form the required solid-statedevice.

TABLE 5 Selective Etching for Pattern Transfers Using PDPP and GLPDPPMasks Etch Selectivity Mask (Material Material Etched:Mask Material NotMaterial Not Etched Etched Etched) Etching Process SiO₂ PDPP >30:1Fluorine Reactive Ion SiO₂ PDPP >30:1 10:1 Buffered Oxide Si PDPP >50:1Fluorine Reactive Ion HgCdTe GLPDPP   10:1 Ar/H/CH₄ Electron CyclotronResonant

Prior art for plasma-deposited photosensitive films from singlecomponent reactants teaches that such films are only sensitive in thedeep ultraviolet end of the spectrum. While this is ideal for highresolution device geometries, that is, under 0.5 μm, there issignificant potential application for photoresists and selective wettingmaterials that are sensitive at longer wavelengths. These resists wouldrequire less expensive lithographic exposure tools. Furthermore, theability to alter the level of photosensitivity of a resist is desirablefor increased processing latitude. Alterable photosensitivity is alsodesirable for applications requiring photosensitivity further into thevisible spectrum, or out of the visible spectrum for higher resolutionpattern replication.

A single three-inch silicon wafer was prepared by the abovemonosilane/ethylene or toluene film depositions to determine PDPP andGLPDPP stoichiometry. The wafer was quartered. One quarter was exposedto 621 mj/sq-cm with light at 365 nm wavelength; one quarter was exposedto 621 mj/sq-cm with light at 254 nm wavelength.

An elemental analysis was performed on portions of the two exposedsamples and one of the unexposed samples. The results are shown in Table6, which indicates a 1:7 atom ratio of silicon to carbon for theunexposed photosensitive film.

TABLE 6 Elemental Analysis for Unexposed and Exposed Samples CarbonOxygen Fluorine Silicon Sample Type (%) (%) (%) (%) Unexposed 77 10 2.311 Exposed to light at 74 16 0 9.7 365 nm wavelength Exposed to light at67 22 2.2 9.2 254 nm wavelength

Portions of both exposed pieces, and one of the quartered unexposedpieces, were submitted to Electron Spectroscopy for Chemical Analysis(ESCA). The ESCA analysis of the binding energies for the exposed andunexposed samples provided the results indicated in Tables 7A, 7B and7C.

TABLE 7A ESCA Binding Energy Data for Unexposed PDPP Samples PeakSiO_(x) Assignments C—R C—OR O═C—OR C→C* C═O,Si—O C—F R—Si (RSi—O)_(n)(1≦ x ≦2) Binding 284.6 285.6 288.4 291.0 532.6 689.6 100.4 102.0 102.8Energy eV Unexposed 71 3.9 0.0 2.0 10 2.3 5.8 5.2 0.0 (Atom Percent)

TABLE 7B ESCA Binding Energy Data for Exposed PDPP Samples at 365 nmPeak SiO_(x) Assignments C—R C—OR O═C—OR C→C* C═O,Si—O C—F R—Si(RSi—O)_(n) (1≦ x ≦2) Binding 284.6 285.6 288.4 291.0 532.6 689.6 100.4102.0 102.8 Energy eV Exposed to 68 4.9 0.0 1.2 16 0.0 3.1 6.6 0.0 lightat 365 nm wavelength (Atom Percent)

TABLE 7C ESCA Binding Energy Data for Exposed PDPP Samples at 254 nmPeak SiO_(x) Assignments C—R C—OR O═C—OR C→C* C═O,Si-O C—F R—Si(RSi—O)_(n) (1≦ x ≦2) Binding 284.6 285.6 288.4 291.0 532.6 689.6 100.4102.0 102.8 Energy eV Exposed to 56 8.6 1.6 0.6 22 2.2 0.0 3.7 5.5 lightat 254 nm wavelength (Atom Percent)

The bonding information is drawn from high resolution scans of theelemental data and was used to examine the nature of the oxygen bondingas well. Atomic percentages are calculated for the included elements anddo not include hydrogen, of which a considerable amount is expected tobe present. The ESCA analysis represents approximately 100 Å of thesurface of the material.

The ESCA analysis indicates photo-oxidation with light at 254 nmwavelength by increased binding of oxygen at that wavelength whencompared to the unexposed sample. The analysis also showsphoto-oxidation with light at 365 nm wavelength not as prominent as thatwith light at 254 nm wavelength. As expected, the incorporation of boundoxygen into the exposed films causes a proportionate reduction in theamount of carbon and silicon present. The binding energy data, from thehigh resolution scans, provides more insight into the photoreaction atthe two frequencies. Peaks which show little significance or are felt tobe attributable to contamination include the 689.6 eV bonds. However,significant trends did develop for the other represented bonds.Significantly, C—C, C—C*, C—H, Si—C, and Si—H bonds showed decreaseswith exposure. Furthermore, C—OC, C—OH, C═O, Si—O bonds showedconsistent increases with exposure to light at 365 and 254 nmwavelengths. It is also noted that with the exposure to light at 254 nmwavelength, all of the silicon present was bonded to oxygen in some formwith no remaining Si—C or Si—H bonds present. The 288.4 eV bond assignedto O═C—OC and O═C—OH are also present with the material exposed to lightat 254 nm wavelength, but not at 365 nm wavelength.

The binding energies assigned to C—R and R—Si are the correct energiesto be predominantly hydrogen bonds. Therefore, substantially no Si—Cbonding is apparent from the analysis for either the unexposed orexposed states. The lack of substantial silicon to carbon bonding isindicative of a film that is not a copolymer of silicon and ahydrocarbon but comprises (Si—H) and (Si—Si) low molecular weightfragments interstitially situated within a substantially organic polymermatrix that does not contain an appreciable amount of silicon and doesnot exhibit highly photosensitive behavior.

Not only is little or no Si—C bonding present, but etch characteristicsindicate that the predominant driver of post exposure characteristics isthe oxides of silicon formed and not any incidental oxidation of carbonand hydrogen.

Satisfactory photoreactivity was demonstrated with light at 254 nm and365 nm wavelengths. Subsequent etching in a buffered oxide etchexhibited satisfactory selective etching for samples exposed to bothwavelengths.

The exposed, photo-oxidized areas (GLPDPP) of a film of the presentinvention easily wet with a liquid whereas the non-photo-oxidized areasof a film do not. It is believed that the surface tension of thenon-photo-oxidized areas of the film is such that it does not permit aliquid to wet and adhere to these non-photo-oxidized areas or regions.Any liquid, that is a non-solid and non-gaseous viscous fluid, withsuitable physical properties (e. g. the liquid could not be at atemperature above the melting point of the photosensitive film) shouldbe capable of being used with a film of the present invention in aselective wetting application. Non-limiting examples of suitable liquidwetting agents are buffered oxide etches described above and metalsolutions as described below.

This process of selective GLPDPP wetting is used to selectively depositmaterials with wet chemistry on the film. The exposed photo-oxidizedareas will wet and allow the selective deposition, typically a metal,such as silver or copper in a liquid solution, while the unexposednon-photo-oxidized areas can later be removed with, for example, eitheran organic solvent or a dry etchant with or without photoexposure. Forexample, a chlorine plasma will remove the unexposed area without theneed for an exposure step. Homogeneous chemical reduction can be used todeposit a thin metal film, for example, a thin film of silver, copper,nickel, gold and lead sulfide. A solution of metal ions is mixed withreducing agents to reduce the ions to metal in a homogeneous platingbath. In a typical case, silver would be in an ammoniacal solution ofsilver nitrate. The silver metal is subsequently precipitated by theaddition of a reducing agent. Sugar, Rochelle's salt (sodium potassiumtartrate), or formaldehyde is commonly used as the reducing agent.Similar techniques have also been used to deposit copper, platinum, andlead sulfide. The contacting of a film of the present invention, with aphoto-oxidized pattern of GLPDPP regions or areas and non-photo-oxidizedPDPP regions or areas, for example, by immersion into this metalsolution results in selective wetting of the photo-oxidized GLPDPP areasand the metal adhering only to the GLPDPP areas.

A selective wetting film of the present invention can be used tofabricate a printed circuit board. A layer of PDPP film of the presentinvention is formed from a plasma reaction on a suitable substrate froma silicon donor and an organic precursor as described above. A mask isproduced to delineate the desired printed circuit pattern for thecircuit board. The mask is fabricated to allow for the transmission ofradiated electromagnetic energy in selected regions that will form theprinted circuit on the board. The mask is placed over the layer of PDPPfilm and radiated electromagnetic energy, such as UV light as describedabove, is applied to these selected regions through the mask tophoto-oxidize these regions and form the GLPDPP. The processed layer ofPDPP film, which now consists of selected regions of GLPDPP andnon-photo-oxidized PDPP film is placed in contact with a liquid form ofthe electrically conductive material that will be used to form theprinted circuit, such as a liquid plating solution of silver asdescribed above. The liquid will selectively wet and adhere to theGLPDPP regions and will not adhere to the non-photo-oxidized regions ofthe PDPP film. The dried liquid adhering to the photo-oxidized GLPDPPform the printed circuit paths on the circuit boards.

This selective wetting process will allow a much finer geometry of theprinted circuit over the conventional process, as well as a more costeffective additive process, rather than the costly process of blanketdepositing of the electrically conductive material, and then removing byetching away the unwanted material. Since the conductive metal circuittrace that dried over the GLPDPP must be supported on an electricalinsulator, the remaining GLPDPP under the metal serves as an excellentsubstrate electrical insulator. The non-photo-oxidized regions of thePDPP film can remain to form an electrically insulating layer over thebase substrate. Alternatively, the non-photo-oxidized regions of thePDPP film may be removed by a suitable method, such as etching away thenon-photo-oxidized regions as described above, or the base substrate maybe removed so that the layer of PDPP film, with non-photo-oxidizedregions and photo-oxidized regions, serves as the circuit board.

The disclosed process of printed circuit board fabrication can beapplied to boards with single-sided patterns, double-sided patterns, andmulti-layer printed wiring applications.

A selective wetting film of the present invention can be used tofabricate a photomask having selective light transparent regions andnon-light transparent regions through which integrated circuit imagesare optically transferred onto a semiconductor wafer. A layer of PDPPfilm of the present invention is formed from a plasma reaction on anoptically transparent substrate, such as glass or quartz, from a silicondonor and an organic precursor as described above. A mask is produced todelineate the desired pattern for the integrated circuit images thatwill be transferred to the wafer. The mask is fabricated to allow forthe transmission of radiated electromagnetic energy to the regions thatwill be non-light transparent in the photomask. The mask is placed overthe layer of PDPP film and radiated electromagnetic energy, such as UVlight as described above, is applied to these selected regions throughthe mask to photo-oxidize these regions and form the GLPDPP. Theprocessed layer of PDPP film, which now consists of selected regions ofGLPDPP and non-photo-oxidized PDPP film is placed in contact with aliquid, for example, a metal plating solution as described above, or anyliquid that will dry to a non-light transparent material. The liquidwill selectively wet, adhere to, and dry over the GLPDPP regions andwill not adhere to the non-photo-oxidized regions of the PDPP film. Thenon-photo-oxidized PDPP regions of the film can be etched away by usingone of the etching processes described above to complete fabrication ofthe photomask by forming the selective light transparent regions of thephotomask.

As described above, selective wetting of photo-oxidized regions of thefilms in the present invention with a buffered oxide etch were used toetch away photo-oxidized regions of the films.

In this disclosure, there is described preferred embodiments of theinvention, it is to be understood that the invention is capable of usein other combinations and enviornments and is capable of changes ormodifications within the scope of the inventive concept as expressedherein. Therefore, the present invention should not be limited to anysingle embodiment, but rather construed in breadth and scope inaccordance with the recitation of the appended claims.

1. A process for selectively wetting a film on a substrate, the processcomprising the steps of: forming the film on the substrate from atwo-component plasma reaction in a substantially air-evacuated plasmachamber, a first component of the two-component plasma reactioncomprising a non-carbon containing and non-oxygenated silicon donor, anda second component of the two-component plasma reaction comprising anon-silicon containing and non-oxygenated organic precursor; patterningthe film with a radiated electromagnetic energy through a mask in thepresence of oxygen to produce a one or more photo-oxidized regions fromexposure to the radiated electromagnetic energy through the mask; andcontacting the film with a liquid, whereby the liquid selectively wetsand adheres to the one or more photo-oxidized regions.
 2. The process ofclaim 1 wherein the liquid is an electrically conductive material. 3.The process of claim 2 further comprising the step of drying theelectrically conductive material adhering to the one or morephoto-oxidized regions to form a printed circuit.
 4. The process ofclaim 2 wherein the electrically conductive material is a solution ofmetal ions and reducing agents.
 5. The process of claim 4 wherein themetal ions are silver ions.
 6. The process of claim 1 wherein the liquidis a buffered oxide etch.
 7. The process of claim 1 wherein the secondcomponent of the two-component plasma reaction is selected from thegroup consisting of ethylene, methane, ethane and toluene.
 8. Theprocess of claim 1 wherein the first component of the two-componentplasma reaction is selected from the group consisting of monosilane,disilane and dichlorosilane.
 9. The process of claim 3 wherein thesecond component of the two-component plasma reaction is selected fromthe group consisting of ethylene, methane, ethane and toluene.
 10. Theprocess of claim 3 wherein the first component of the two-componentplasma reaction is selected from the group consisting of monosilane,disilane and dichlorosilane.
 11. A process for forming a photomaskcomprising the steps of: forming a film on an optically transparentsubstrate from a two-component plasma reaction in a substantiallyair-evacuated plasma chamber, a first component of the two-componentplasma reaction comprising a non-carbon containing and non-oxygenatedsilicon donor, and a second component of the two-component plasmareaction comprising a non-silicon containing and non-oxygenated organicprecursor; patterning the film with a radiated electromagnetic energythrough a mask in the presence of oxygen to produce a one or morephoto-oxidized regions from exposure to the radiated electromagneticenergy through the mask; contacting the film with a non-transparentliquid, whereby the non-transparent liquid selectively wets and adheresto the one or more photo-oxidized regions; drying the non-transparentliquid adhering to the one or more photo-oxidized regions to produce aone or more non-transparent regions on the film; and etching away thefilm in regions not included in the one or more non-transparent regionsto form the photomask.
 12. The process of claim 11 wherein the secondcomponent of the two-component plasma reaction is selected from thegroup consisting of alkanes, alkenes, alkynes, phenyls and aromatichydrocarbons.
 13. The process of claim 11 wherein the second componentof the two-component plasma reaction is selected from the groupconsisting of ethylene, methane, ethane and toluene.
 14. The process ofclaim 11 wherein the first component is selected from the groupconsisting of monosilane, disilane and dichlorosilane.
 15. The processof claim 14 wherein the second component is selected from the groupconsisting of ethylene, methane, ethane and toluene.
 16. The process ofclaim 11 wherein the non-transparent liquid is a metal plating solution.17. A process for selectively wetting a photosensitive film on asubstrate, the process comprising the steps of: forming thephotosensitive film on the substrate from a two-component plasmareaction in a substantially air-evacuated plasma chamber, a firstcomponent of the two-component plasma reaction comprising a non-carboncontaining and non-oxygenated silicon donor, and a second component ofthe two-component plasma reaction comprising a non-silicon containingand non-oxygenated organic precursor; the photosensitive film comprisingphotosensitive (Si—H) and (Si—Si) fragments situated in a non-siliconcontaining and non-photosensitive organic polymer matrix; patterning thefilm with a radiated electromagnetic energy through a mask in thepresence of oxygen to produce a one or more photo-oxidized regions fromexposure to the radiated electromagnetic energy through the mask to formsilicon oxides from oxidation of silicon in the (Si—H) and (Si—Si)fragments; and contacting the film with a liquid, whereby the liquidselectively wets and adheres to the one or more photo-oxidized regions.18. The process of claim 17 wherein the second component of thetwo-component plasma reaction is selected from the group consisting ofethylene, methane, ethane and toluene.
 19. The process of claim 17wherein the first component of the two-component plasma reaction isselected from the group consisting of monosilane, disilane anddichlorosilane.
 20. The process of claim 19 wherein the second componentof the two-component plasma reaction is selected from the groupconsisting of ethylene, methane, ethane and toluene.
 21. A process forselectively wetting a film on a substrate, the process comprising thesteps of: forming the film on the substrate from a two-component plasmareaction in a substantially air-evacuated plasma chamber, a firstcomponent of the two-component plasma reaction comprising a non-carboncontaining and non-oxygenated silicon donor, and a second component ofthe two-component plasma reaction comprising a non-silicon containingand non-oxygenated organic precursor; patterning the film with aradiated electromagnetic energy through a mask in the presence of oxygento produce a one or more photo-oxidized regions from exposure to theradiated electromagnetic energy through the mask; and contacting thefilm with an electrically conductive liquid, whereby the electricallyconductive liquid selectively wets and adheres to the one or morephoto-oxidized regions.
 22. The process of claim 21 further comprisingthe step of drying the electrically conductive liquid adhering to theone or more photo-oxidized regions to form a printed circuit.
 23. Theprocess of claim 21 wherein the electrically conductive liquid is asolution of metal ions and reducing agents.
 24. The process of claim 23wherein the metal ions are silver ions.
 25. A process for forming aphotomask comprising the steps of: forming a film on an opticallytransparent substrate from a two-component plasma reaction in asubstantially air-evacuated plasma chamber, a first component of thetwo-component plasma reaction comprising a non-carbon containing andnon-oxygenated silicon donor, and a second component of thetwo-component plasma reaction comprising a non-silicon containing andnon-oxygenated organic precursor; patterning the film with a radiatedelectromagnetic energy through a mask in the presence of oxygen toproduce a one or more photo-oxidized regions from exposure to theradiated electromagnetic energy through the mask; contacting the filmwith a metal plating solution, whereby the metal plating solutionselectively wets and adheres to the one or more photo-oxidized regions;drying the metal plating solution adhering to the one or morephoto-oxidized regions to produce a one or more metal plated regions onthe film; and etching away the film in regions not included in the oneor more metal plated regions to form the photomask.